This invention relates to diamond and more particularly to diamond produced by chemical vapour deposition (hereinafter referred to as CVD).
Methods of depositing materials such as diamond on a substrate by CVD are now well established and have been described extensively in the patent and other literature. Where diamond is being deposited on a substrate, the method generally involves providing a gas mixture which, on dissociation, can provide hydrogen or a halogen (e.g. F,Cl) in atomic form and C or carbon-containing radicals and other reactive species, e.g. CHx, CFx wherein x can be 1 to 4. In addition, oxygen-containing sources may be present, as may sources for nitrogen, and for boron. In many processes inert gases such as helium, neon or argon are also present. Thus, a typical source gas mixture will contain hydrocarbons CxHy wherein x and y can each be 1 to 10 or halocarbons CxHyHal2 (Hal=halogen) wherein x and z can each be 1 to 10 and y can be 0 to 10 and optionally one or more of the following: COx, wherein x can be 0.5 to 2, O2, H2, N2, NH3, B2H6 and an inert gas. Each gas may be present in its natural isotopic ratio, or the relative isotopic ratios may be artificially controlled; for example hydrogen may be present as deuterium or tritium, and carbon may be present as 12C or 13C. Dissociation of the source gas mixture is brought about by an energy source such as microwaves, RF energy, a flame, a hot filament, or a jet based technique and the reactive gas species so produced are allowed to deposit onto a substrate and form diamond.
CVD diamond may be produced on a variety of substrates. Depending on the nature of the substrate and details of the process chemistry, polycrystalline or single crystal CVD diamond may be produced. The production of homoepitaxial CVD diamond layers has been reported in the literature. Prior art has generally concerned itself with the thermal, optical and mechanical properties of CVD diamond.